The present invention relates to a semiconductor laser device provided with a semiconductor laser diode which outputs laser light having a plurality of oscillation vertical modes, a semiconductor laser module, and a semiconductor laser control method.
In recent years, as a result of the rapid rise in popularity of the Internet and the rapid increase in internal LAN connections inside businesses and the like, there have been problems not only with the increase in the number of communication calls, but also with the increase in data traffic that has accompanied the increasing volume of data contents being transferred. Therefore, in order to prevent a drop in communication performance caused by these problems, wavelength division multiplexing (WDM) systems have undergone remarkable development and are in widespread use.
In a WDM system, by placing a plurality of optical signals on respectively different wavelengths, a hundred-fold increase over the conventional volume of data transfer has been achieved using a single optical fiber. In particular, by performing light amplification using erbium doped fiber amplifiers (EDFA) and Raman amplifiers, existing WDM systems become capable of long distance broadband transmissions. Here, an EDFA is a concentrated type of optical fiber amplifier that employs the principle of the light of a transmission signal in the 1550 nm wavelength band being amplified inside a special optical fiber that is doped with the element erbium and has excitation laser light having a 1480 nm wavelength or a 980 nm wavelength passed therethrough. A Raman amplifier, on the other hand, is a distribution type optical fiber amplifier that uses stimulated Raman scattering and that acts as an amplifying medium to enable an existing optical fiber to amplify signal light in its existing state.
Accordingly, in a WDM system, it is essential to achieve highly accurate oscillation control as well as high output operation for both a light source for a signal that creates a light signal itself, and also for an excitation light source used in the above described optical fiber amplifiers. In particular, it is desirable that the light source for a signal and the excitation light source can be obtained using a semiconductor laser diode, and that the signal modulation and amplification degree can be controlled electrically.
In a semiconductor laser diode used as a signal light source, in order to make the faster transmission of a greater volume of information possible, a direct modulation method in which an injection current applied to the semiconductor laser diode is modulated by a signal is often used. However, in this method, the problem of what is known as xe2x80x9cwavelength chirpingxe2x80x9d exists. Wavelength chirping has a cycle of, variation in the carrier density in the active layer caused by changes in the injection currentxe2x86x92variation in the refractive indexxe2x86x92variation in the oscillation wavelength. Therefore, currently, what are known as xe2x80x9cmodulator integrated light sourcesxe2x80x9d, in which a semiconductor laser diode and a semiconductor light modulator are integrated on the same substrate, are being developed. In a modulator integrated light source, in order for modulation to be performed by a semiconductor light modulator section, no variation in the injection current in the semiconductor laser diode section is generated, and thus the above described problem of wavelength chirping is avoided.
It is an object of the present invention to provide a semiconductor laser device in which the injection current of the semiconductor laser diode is fixed, a semiconductor laser module, and a semiconductor laser control method by providing a semiconductor laser diode that outputs laser light having a plurality of oscillation vertical modes, and by integrating a light amplifier and a light attenuator on the same substrate as the semiconductor laser diode.
According to one aspect of the present invention, a semiconductor laser device, comprising, a semiconductor laser diode section that generates laser light having a plurality of oscillation vertical modes that are below a predetermined output value using wavelength selection properties of a diffraction grating formed adjacent to an active layer and between a reflective end surface and an emission end surface of laser light, and a semiconductor light adjustment section that is integrated on the same semiconductor substrate on which the semiconductor laser diode section is formed, and that adjusts an output of the laser light.
According to this aspect, it is possible for a semiconductor laser diode section to generate laser light having a plurality of oscillation vertical modes whose peaks are below a predetermined output value such as the threshold value at which stimulated Brillouin scattering is generated, and for the output power of this laser light to be adjusted by a semiconductor light adjustment section that is integrated on the same substrate as that of the semiconductor laser diode section.
According to another aspect of the present invention, a semiconductor laser module, comprising, the above described semiconductor laser device, an optical fiber which guides laser light emitted from the semiconductor laser device to the outside, and an optical coupling lens system which optically couples the semiconductor laser device with the optical fiber.
According to this aspect, the above described semiconductor laser device can be provided sealed in a package casing.
According to still another aspect of present invention, a semiconductor laser control method that controls an output of laser light from the above described semiconductor laser device, comprising, a step of fixing a current applied to the semiconductor laser diode section, and a step of adjusting a current or voltage applied to the semiconductor light adjustment section.
According to this aspect, it is possible to adjust and then output the output power of the laser light to be finally output while varying the injection current of the semiconductor laser diode section.